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Transformers + Substations Handbook: 2014
with great accuracy the voltage in all critical points. The characteristics
of the transformer response for ordinary lightning impulse and chopped
waves (not involving VFT voltages) are shown in
Figures 3
and
4
and
offer a simple analysis that most software employed in review of
equipment design is able to handle.
Figures 5
and
6
show the response of the transformer under a
chopped wave impulse test.
Figure 6
defines the response at a spe-
cific point of the winding. This view is only achievable with specific
software.
Figure 6: Simulation – chopped wave impulse on the air: difference
between disc 1 and 2 2 (n°49 = points 45 and 40).
Figure 5: Simulation – chopped wave on the air.
Figure 4: Standard chopped impulse wave.
Figure 3: Standard lightning impulse wave.
Front time:
T
s
=
1.2
± 0.36 µs
Time of half value:
T
r
= 50 ± 10 µs
Front time:
T
s
=
1.2
± 0.36 µs
Chopping time:
T
c
=
2
µs to
6
µs
VOLTAGE TO GROUND
VOLTAGE DIFFERENCE
The presence of overvoltages on the GIS system is a result
of the operation of the switching devices.